What is beta-carotene? How does it affect cancer?

Cancers treated or prevented: Studies have found that a diet high in fruits and vegetables containing beta-carotene reduces the risk of certain types of cancer, including those of the prostate and lung. Researchers believe that beta-carotene and other antioxidants in fruits and vegetables work together to lower cancer risk.

It was thought that beta-carotene supplements might reduce the risk of certain cancers, especially lung cancer, but according to the American Cancer Society, there is no evidence of any cancer preventive benefit when beta-carotene is taken alone in supplement form. In fact, studies have found that smokers and people who have been exposed to asbestos who take beta-carotene supplements have a significantly higher risk of developing lung cancer and of dying from their cancer than those who do not take the supplements.

Scientific evidence for beta-carotene elevating the risk of prostate cancer in men has been inconclusive. For instance, the National Cancer Institute’s Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (1992–2001) found that men with the highest levels of beta-carotene in their blood were at increased risk for developing more aggressive and deadly prostate cancer. However, 2009 follow-up results from the long-term Carotene and Retinol Efficacy Trial (1983–95) reported neither positive nor negative effects of beta-carotene supplementation on the rate of new prostate cancer cases.

Delivery routes: Oral in capsule and tablet forms. The US National Library of Medicine reports that eating five servings of fruits and vegetables daily provides six to eight milligrams of beta-carotene.

How this substance works: Beta-carotene is an antioxidant. It protects cells and deoxyribonucleic acid (DNA) from damage caused by unstable molecules called "free radicals," which are produced during metabolic processes as cells burn up oxygen for energy. Free radicals are believed to contribute to cancer and other diseases. Vitamin A, which the body produces from beta-carotene, helps prevent the uncontrolled cell growth that occurs with cancer.

Side effects: Beta-carotene may increase the risk of lung cancer or prostate cancer in people who smoke or drink alcohol heavily or who have been exposed to asbestos. It also may increase the risk of more aggressive prostate cancers. In high doses, beta-carotene may interact with some types of chemotherapy drugs or radiation.

Bibliography

"Antioxidants and Cancer Prevention." Cancer.gov. Natl. Cancer Inst., Natl. Inst. of Health, 16 Jan. 2014. Web. 8 Sept. 2014.

The ATBC Cancer Prevention Study Group. "The Effect of Vitamin E and Beta Carotene on the Incidence of Lung Cancer and Other Changes in Male Smokers." New England Journal of Medicine 330.15 (1994): 1029–35. PDF file.

"Beta-Carotene." MedlinePlus. US Natl. Lib. of Medicine, 19 July 2011. Web. 8 Sept. 2014.

Calvagna, Mary, and Brian Randall. "Vitamin A." Health Library. EBSCO, Feb. 2013. Web. 8 Sept. 2014.

"Vitamin A, Retinoids, and Provitamin A Carotenoids." Cancer.org. Amer. Cancer Soc., 2 Apr. 2012. Web. 8 Sept. 2014.